The present invention relates to apparatus and methods for producing both heat and electrical power by burning fuels, and more particularly to apparatus and methods for producing both heat and electrical power from a fuel-burning stove, boiler, or furnace.
A need has long existed for a practical, clean, easy-to-operate, reliable, and inexpensive method to provide heat and electricity for residential housing in rural locations and in developing nations. A wood-burning or coal-burning stove or furnace is one of the most widely used heating devices in rural areas of the USA as well as in many other relatively undeveloped areas, especially in cold regions and highlands. Such a furnace or stove has the advantages of simple design and low cost. Also, it may use local biofuel and does not significantly increase the natural level of carbon dioxide released to the atmosphere. Hot-water and steam boilers have become increasingly popular for family homes in recent years. They provide for radiant and convective heating systems, laundry, bathing, and cooking, as well as provide for air-conditioning and refrigeration by driving absorption coolers. They can also be adapted for use with garages, pools, greenhouses, and the like.
In small, single-family devices, it is customary to circulate hot water using electrically-powered pumps, the power required for one pump often being between 200 and 1000 watts, depending on the model and the length of piping required. When such a heating device is operated continuously, especially under cold or winter conditions, the cost of power consumed by the pump can approach the cost of fuel. Additionally, outages of electrical service caused by natural forces or other factors may put such a furnace out of action and create a grave situation for the user. Battery power or backup emergency gasoline power generation is an expensive alternative.
Thus, attempts have been made to develop devices that utilize waste heat, normally exhausted in flue gases, to produce electricity. Such a source of electricity could be used to pump water in a hot water system, supply power to a local utility grid, or perform other useful work. It could also provide electrical energy to be stored, for example in electrical storage batteries, for future use.
A number of attempts to develop devices that utilize the heat of normally-rejected stack gases to produce electricity have been made over many years. Two basic approaches were under investigation: the first approach employing closed cycle devices such as the Stirling engine, and the second approach employing open cycle devices, such as gas turbines. Both approaches have largely proved to be unsuccessful. In the first case, a high gas temperature (more than 1500xc2x0 K.) was needed. Such a temperature cannot practically be reached in the combustion area of a wood or coal furnace. In the second case, a high pressure was needed inside a furnace, and also the fuel combustion products quickly clogged the turbine(s).
Because of the above described problems, an effective device that can provide an electrical power supply by utilizing heat released in the furnace of a heating stove, water heater, or boiler has not yet been created. The present invention combines elements into a new configuration that unites a heater or water boiler with a microturbine in such a way that the microturbine working fluid (normally air) is heated by the heat of stack gases with the help of a novel surface heat exchanger located inside the boiler or furnace.
Accordingly, objects of the present invention include apparatus and methods for producing both heat and electrical energy by combusting fuels with an oxygen-containing material (normally air) in a stove or boiler using a novel arrangement of a surface heat exchanger and microturbine-powered generator. The equipment is particularly suited for use in rural and relatively undeveloped areas, especially in cold regions and highlands. Although air is commonly used in this combustion process, other oxygen-containing materials such as other oxygen-containing gas mixtures may be used in special applications where such oxygen-containing mixtures are available, including undersea laboratories and space stations. Further and other objects of the present invention will become apparent from the description contained herein.
In accordance with one aspect of the present invention, the foregoing and other objects are achieved by a fuel-burning, electricity-producing apparatus for providing both heat and electrical power by combusting a fuel and an oxygen-containing material which comprises: an essentially closed enclosure further comprising enclosure walls, and suitably configured for combusting a fuel and an oxygen-containing material to produce a flue gas, the enclosure further comprising means for admitting fuel; a first oxygen-containing material duct means for admitting cool oxygen-containing material further comprising a conduit configured and disposed to admit oxygen-containing material at one end and deliver oxygen-containing material to a turbine-generator means at the other end; turbine-generator means further comprising a gas turbine means, a generator means further comprising means to electrically connect said generator means to an electrical load, and a gas compressor means, said turbine means, said generator means, and said gas compressor means being mechanically linked together to operate concurrently, and being configured and disposed to accept cool oxygen-containing material from said first oxygen-containing material duct means, pass the cool oxygen-containing material through said gas compressor, and discharge the cool, compressed oxygen-containing material from said gas compressor; heat exchanger means further comprising a first conduit and a second conduit suitably arranged for heat transfer therebetween, said first conduit for the oxygen-containing material stream configured and disposed to accept cool oxygen-containing material from the compressor discharge of said turbine generator means, pass the oxygen-containing material therethrough to heat the oxygen-containing material, and a second conduit having a surface exposed to flue gas, to accept flue gas from the combustion of the fuel and oxygen-containing material, pass the flue gas therethrough, thus transferring heat from the flue gas stream to the oxygen-containing material stream to produce heated oxygen-containing material; a second oxygen-containing material duct means for conducting heated oxygen-containing material further comprising a conduit configured and disposed to accept heated oxygen-containing material from said heat exchanger and pass the heated oxygen-containing material therethrough and into said enclosure for combustion with the fuel material; and flue gas discharge duct means for receiving flue gas from the discharge of said second conduit of said heat transfer means, conducting the flue gas therethrough, and discharging the flue gas from said enclosure; the entire arrangement being configured so that oxygen-containing material is brought from outside said enclosure, into said enclosure for combustion, and the flue gas is brought from inside said enclosure where combustion occurs, and out of said enclosure for discharge from said enclosure.
In accordance with another aspect of the present invention, a method for providing both heat and electrical power by combusting a fuel and an oxygen-containing material comprises the steps of: providing a fuel-burning, electricity-producing apparatus comprising an essentially closed enclosure further comprising enclosure walls, and suitably configured for combusting a fuel and an oxygen-containing material to produce a flue gas, the enclosure further comprising means for admitting fuel; a first oxygen-containing material duct means for admitting cool oxygen-containing material further comprising a conduit configured and disposed to admit oxygen-containing material at one end and deliver oxygen-containing material to a turbine-generator means at the other end; turbine-generator means further comprising a gas turbine means, a generator means further comprising means to electrically connect said generator means to an electrical load, and a gas compressor means, said turbine means, said generator means, and said gas compressor means being mechanically linked together to operate concurrently, and being configured and disposed to accept cool oxygen-containing material from said first oxygen-containing material duct means, pass the cool oxygen-containing material through said gas compressor, and discharge the cool, compressed oxygen-containing material from said gas compressor; heat exchanger means further comprising a first conduit and a second conduit suitably arranged for heat transfer therebetween, said first conduit for the oxygen-containing material stream configured and disposed to accept cool oxygen-containing material from the compressor discharge of said turbine generator means, pass the oxygen-containing material therethrough to heat the oxygen-containing material, and a second conduit having a surface exposed to flue gas, to accept flue gas from the combustion of the fuel and oxygen-containing material, pass the flue gas therethrough, thus transferring heat from the flue gas stream to the oxygen-containing material stream to produce heated oxygen-containing material; a second oxygen-containing material duct means for conducting heated oxygen-containing material further comprising a conduit configured and disposed to accept heated oxygen-containing material from said heat exchanger and pass the heated oxygen-containing material therethrough and into said enclosure for combustion with the fuel material; and flue gas discharge duct means for receiving flue gas from the discharge of said second conduit of said heat transfer means, conducting the flue gas therethrough, and discharging the flue gas from said enclosure; the entire arrangement being configured so that oxygen-containing material is brought from outside said enclosure, into said enclosure for combustion, and the flue gas is brought from inside said enclosure where combustion occurrs, and out of said enclosure for discharge from said enclosure; admitting fuel into said combustion area; admitting oxygen-containing material into and through said first oxygen-containing duct means, through said compressor means for compression, through said first conduit of said heat exchanger for heating, through said turbine means, and through said second oxygen-containing duct means to said combustion area, the heated oxygen-containing material providing energy input into said turbine means to rotate said compressor means and said generator means; combusting the fuel with the oxygen-containing material within said combustion area to produce flue gas and heat energy; conducting the flue gas through said second conduit of said heat exchanger to heat cool oxygen-containing material to provide heated oxygen-containing material and further conducting the flue gas from said heat exchanger through said flue gas discharge means and from said enclosure; and operating said generator means to produce electrical energy.